Side mount or Doubles (Twinsets) for photography

I am thinking of upgrading my dive equipment to provide greater redundancy underwater.

I am somewhat loathe to acquire a set of doubles or twinsets due to the weight issues involved, as well as the perceived difficulty in manipulating the manifold in times of emergency. As a result, I am watching the development of the side mount rig as an alternative to the traditional doubles/twinset rig.

My dive profile is recreational, freshwater mostly, cold to very cold water, very rarely in confined spaces, visibility sometimes very limited, with strong current at times.

As a side note, rebreathers are intriguing, but after having an acquaintance expire due to an incident involving a rebreather, I have decided to relegate rebreather technology to the bottom of the list until I can satisfy myself to their safety record. An off-the-cuff risk-benefit analysis still doesn't pass muster for me, as far as I'm concerned. Perceived risk still outweighs perceived benefits for me, at this point.

I would like to hear opinions from other photographers who have experience with both setups as to their likes and dislikes for both systems.

Thanks.

Hi Polliwog,

May we first establish the fundamental similarities, advantages and differences between indes (sidemount) and manifolded twins?

1. It is probably a good idea to breathe down indes in increments which allows you to both monitor system performance and provide the maximum available gas in an emergency but increases workload

2. If an inde should fail, you only have the remaining gas available in the other cylinder.

3. Its easy to breathe down one inde to almost nil and the other to around half which allows you to replace just one cylinder for a 'two tanker'

4. Twins are breathed as if one cylinder therefore reducing workload.

5. If an element of a twin cylinder should fail, i.e. manifold, HP hose, freeflow second stage or first stage a shutdown is required. But when completed you will have all your remaining back gas available.

6. For the second dive, you may need a second twin set.

I guess that on balance, for recreational depths, indes either back or slung may be better. For tech or deco, manifolded are preferred.

Moi? I use all manifolded twins from sevens, tens, twelves and fifteens. My poor little brain can only manage one system...

Hi Paul,

I regularly dive and shoot with a DSLR in doubles with an isolation manifold, but the only "sidemount" experience I have is carrying stage bottles (AL 80's) and deco bottles (AL 40's).

I think Timmoranuk explained things very well, although I have a minor comment on #5. If you have an actual manifold failure, and have to close a post and the isolator, you only have the gas remaining in the tank you're still breathing from - the point is a bit moot, because a failure of that magnitude would signal the end of the dive anyway.

One of the immediate benefits to having your redundancy built into the rig on your back, is that it is largely out of the way of you shooting. No bottles up-front means lots of space for the camera and you to work. I'm not sure what the sidemount folks would say, but even a deco or stage bottle upfront can be a little in the way at times. I've gotten used to it, but its something to consider.

Also, I rarely find the weight of a set of doubles to be an issue - in fact, I now prefer it to single tank diving if for no other reason than 12 lbs on the belt is a lot more comfortable than 26! In FW with steel doubles - assuming you are in a drysuit and wearing a wing/BC, you'd likely not need much weight on the belt at all.

The other option is to wear a pony bottle. Someof the solo divers out this way tend to use them, usually an AL 30 (sometimes a 19) and only use it to get themselves to the surface if something goes wrong with the primary gas supply. As you probably know, the trick to making that work is to know your SAC rate and then calculate from what max depth you could make a safe, controlled ascent - including a safety stop, then never go below that depth.

As for being able to reach the valves, that just takes practice. Anytime I'm sitting around, I alternate having my arms folded behind my head like I'm reaching for a valve in order to keep stretching the appropriate muscles. Apparently, reaching back for the top-side of the head rest in your car/truck is also a good way to develope the needed flexibility (best done only at stop lights... that are red).

I'll wrap up by saying I really enjoy the peace of mind I have while diving backmounted doubles, but they do incurr some responsibility on the part of the diver in order to get the most out of them, and like Timmoranuk, I can only handle one system too - especially while trying to shoot!

Hopefully, the folks with real sidemount experience can/will add to this for a more balanced perspective!

Hope this helps, and good luck with whatever you decide.

Lee

"I think Timmoranuk explained things very well, although I have a minor comment on #5. If you have an actual manifold failure, and have to close a post and the isolator, you only have the gas remaining in the tank you're still breathing from - the point is a bit moot, because a failure of that magnitude would signal the end of the dive anyway."

Agreed! But use a manifold with captive o-rings and that should never be a problem ( what can possibly go wrong... ? hehehe ).

A 3 litre pony is the minimum bail out you should have considering that you have no deco on the clock and you are prepared to forgo your optional (?) safety stop. Frankly, when diving singles, I can't be arsed to mount a pony and sometimes I have to take 20 minutes at 3 metres if I cant get a nitrox fill... ( but what can possibly go wrong? hehehe ). I service my own gear, so I suppose that modifies my confidence but like you, I am less keen on singles these days...

Side-slungs I find less convenient for shooting and contact with the bottom for some angles can be an issue. Inverted, head down positions are a little less comfortable too but I do confess this may be probably due to my lower experience with side-slungs than back gas.

Yes, hoping you side-slung guys will chip in too :-)

Later, Tim

twin indies work great, especially if you go diving abroad and all you need are 2 of their standard cylinders, I've travelled abroad with this set up about 8 times now, never had a problem, the only extra weight you need is another set of regs and cambands on your wing

I use twin high-pressure 7l cylinders with a manifold in green water, and single cylinders in blue. The larger cylinders hired on most dive boats can be awkward to use: I've noticed some divers use a lot of air and effort when using independent twins. I've never seen side mounts as a primary rig except in enclosed spaces, caves and wrecks. When I've used side mounts as stage bottles adding a camera has seemed a step too far, but I suppose my discomfort could be inexperience as I haven't gone to that extreme on many occasions.

If you use manifolded twins, have a regulator failure and do a proper shut-down drill, then some of the gas on the leaky side can be saved, to breathe when the manifold is opened up again: training and practice are essential!

Tim

I'm a regular sidemount cave diver, and my first observation would be that sidemounts off a small to medium boat are a nightmare. I usually sit in the cave entrance in the water to put mine on, and walking around in them can be impracticable depending on your harness. I wear them so I can get into small caves, but in the water they're also great for photography - I can roll over sideways and shoot up without turning turtle like I would in backmounted steel twins and drysuit. Sidemounts are great for the "too heavy on land" problem because you can carry them one at a time.

Backmounted independents create more task loading than a manifold during your average dive, as you have to switch regs regularly to decant evenly. In an emergency though, switch to the reg that works and leave. Manifolded twins are easier most of the time - no reg switching - but in an emergency you must respond immediately to save your gas. I'm not sure why people think that if they can't handle reg switching most of the time, they'll magically be able to handle valve shutdowns when it all goes wrong. Check out the graphs at the bottom of this article to see how much time you have to shut down your manifold. If you can't do it within that limit, you're on a single tank with additional failure points and a misplaced sense of complacency. Understand your life support equipment!

Steel twins are heavier underwater, and you won't need as much lead. They do slow you down swimming into current which might be a concern for you. For travel, you can carry rigging to create independent or sidemounted twins from hired single tanks without much fuss at all. For diving at home, a pony might be enough to add the redundancy you're looking for.

Thanks for all the great replies.

I'm still a little undecided, but think I'll start using an aluminum 80 as a stage bottle and progress through to a full side mount rig(I assume I will be able to re-configure my Transpac BC for it). It seems to be the cheapest way to go at the moment. As for the doubles set up, I think I will see if I can beg, borrow, or steal a set for a few dives and make my choice at that point.

errbrr -- That article certainly presents a forceful argument and outlines a number of my concerns, as well as touching on the use of doubles with valves mounted on the bottom of the tanks (something I would like to find more information about).

I have dived extensively with manifolded doubles, independent doubles and side-mounted doubles. Although side-mounted aluminium cylinders leave you feeling very unrestricted, they do get in the way a little with a big camera rig. However, as you say you dive in cold fresh water, with side-mounted tanks, should a regulator go into free-flow you still have access to ALL the gas in that tank simply by opening its valve each time you want to inhale off your regulator, then closing it during the exhale phase.

As for using side-mounts in a small boat, it's very convenient. Sitting on a sponson, you clip each tank to the top D-rings, lift up the bottoms and clip on the lower and fall back in the water. No travelling with a heavy double-set on your back or lifting a heavy set up on to the tubes before you struggle in to it.

I have just finished in Truk using independent back-mounted twins. These have given me a lot of strategy regarding gases as well as offering simplicity in pairing up tanks (they don't even have to be the same size!). On dives on the 50-60m range, I used a bottom mix in one and a light deco-mix of Nitrox30 in the other. I started with the regulator from the bottom mix in my mouth and switched to Nirox30 at 40m on the way up. To those that say I'm taking one tank blow its MOD, I say what difference is there if it's slung? If I have a catastrophic failure of my bottom mix regulator, I will breathe the Nitrox30 for the short time on the way up to 40m from 55m. I would rather breathe O2 for a short time at ppo2 of 2 bar than water.

Manifolds are de rigeur with some training agencies. After many years of using a manifolded set, I concluded it was useful when filling and carrying the tanks and of course introduces the magic skill of the shut-down drill but for not much else.

So I would side-mount if I were you!

''As for using side-mounts in a small boat, it's very convenient. Sitting on a sponson, you clip each tank to the top D-rings, lift up the bottoms and clip on the lower and fall back in the water. No travelling with a heavy double-set on your back or lifting a heavy set up on to the tubes before you struggle in to it.''

I would agree with this. In a small zodiac in heavy seas sidemounts can be very convenient both to don and doff.

Although we use a slightly different strategy, in that all our gas goes via a manifold which is pluggable via a QC6 fitting. This makes life even easier as you can clip the cylinder to a tag line and drop it overboard and plug in when in the water. This means there is no need to be on a small pitching boat carrying the weight of a cylinder.

The advantage of manifolds (whether sidemount or back mount) is that you always have a donate-able long hose in the case of a team emergency. With independent doubles you don t get the same seamless emergency protocol as you are deploying stuffed hoses or regulators from another cylinder etc.

At the end of the day it is a philosophical point. If you dive within a team then manifolds provide the easiest way to manage an emergency (which should be your priority). If you don t believe in team diving then, it is immaterial as you gear and gas are solely your province, but conversely there is no-one to save your bacon either. Plenty of ways to skin a cat, but you need to make a choice about the most suitable way to dive.

E

I'd like to add the rider that, recently, I was shown a different 'right' way to sidemount by a cave diver and it is my opinion that although it makes the diver look pretty, the tanks are rigged so high up under the arms that they get in the way when using a full-size camera rig. Not only that, but they are hooked on at the bottom and rely on the bungee to hold them at the top, thereby making them much more difficult to rig in a small boat. So sidemounting depends on who you are taught by!

I'm a regular sidemount cave diver, and my first observation would be that sidemounts off a small to medium boat are a nightmare.

So where are you cave diving out of a boat?

I'd like to add the rider that, recently, I was shown a different 'right' way to sidemount by a cave diver and it is my opinion that although it makes the diver look pretty, the tanks are rigged so high up under the arms that they get in the way when using a full-size camera rig. Not only that, but they are hooked on at the bottom and rely on the bungee to hold them at the top, thereby making them much more difficult to rig in a small boat. So sidemounting depends on who you are taught by!

To me sidemount is an addition to your diving tool box, rather than a trendy way to wear tanks. It has certain advantages over back mount and certain drawbacks.

One of the distinct advantages of sidemount is the easy and speed of gearing up particularly within small boat operations. So impressive is this that we (Unified Team Diving) recently got the LA Fire Dept Rescue divers interested in using this system as a way to cut down on deployment time, in situations where time really is of the essence.

If you have been demonstrated systems that slow down your gear up and prevent you from handling a camera, I would really be questioning whether this manifestation of sidemount, actually has any advantages over back mount.

My aim is too have a diving tool box full of elegant and easily configurable tools so I can pick the right one for the task at hand, rather than one full of hammers...

I'm too stupid to be able to effectively manage my gas in an independent system and take photographs. With either side mount or back mount independents, remembering to switch regs in order to breathe the cylinders down evenly is too much task loading when I'm focused on taking pictures, or perhaps I'm just too thick to able to operate the system

Unless I'm diving at great depths (in which case, rebreather or big manifolded twins seem to work for me), I use an "H" valved single cylinder. This gives me the redundancy in terms of regulators, without the hassle of additional cylinders. If I have a free flow, I can still shut the offending valve and ascend. It does not increase my gas volume, but then for most photography, this is not something that causes me any concern. If I do need any additional gas volume for some purpose, I can add a side slung bottle of an appropriate size as a bail out bottle.

Adam

Yes, it's a question of using the right tool for the job. I too use an H-valve with a single for shallow UK diving.

The picture that recently did the rounds of two ichthyologists clouting the reef with a sling tank was an obvious case of the wrong tool. Back-mounted keeps the tanks clear of what you might be photographing. As for twins without a manifold, manifolds have been given too much importance by a certain training agency in my view. I can tell you that I can breathe one tank down to zero bar and with the other full, not be diving on one side! In fact it often upsets Internet divers that I sometimes take different mixes in independent twins. One mix for depth and one for accelerated deco. It seems ideal for dives such as the San Francisco Maru. But as I and others said, use the right tool for the job.

+1 for SM in currents... more streamlined

-1 for cold water... steel tanks not ideal. Dry suit does involve complications

Are you diving off a boat or from the shore?

+1 for boat diving: just sit on the side, clip your top boltsnaps and roll back. May be more difficult to do giant stride entries

-1 for shore: getting in & out can be more difficult with multiple tanks. I hold onto my tanks and use them as "walking sticks" when entering Tulamben waters. This is of course made very difficult if you have a full camera rig as well.

Most of my dives are tropical (5mm max), boat dives with aluminum tanks and I choose SM over BM any day. Here is why:

1) Ease of logistics. Any 2 tanks will do. Small spatial footprint on the boat. No refill between dives, just change tanks

2) Trim and position in the water. Very stable once the rig is set up correctly (which can take time and effort)

3) Streamlining. SM with 2 S80's feels a lot more streamlined than 1 S80 with a BCD. Great for diving in current or using proper finning techniques

4) No/less weight required

5) Proper redundancy. I would only use H/Y valves for very shallow dives as this is not a redundant system.

Issues with gas loss in one tank can be minimised by feathering the tank, i.e. closing it when not breathing and opening it only when breathing. This is actually more advantageous than manifolded tanks, unless the leak is coming from the O-ring in the tank neck...